Virtual Pipe Organ Basics - How it is made

Sampling

Sound recording

Sample based virtual pipe organs are recorded using a process called sampling, which is a recording method that involves high-quality audio equipment and meticulous on-site work at the pipe organ.

In this systematic work, every sound the organ makes is recorded individually, note-by-note, pipe-by-pipe. Since pipe organs, especially historic instruments, exhibit time-variant sonic features that make them ‘beautiful’ and ‘living’, these variations in the sound, particularly the transient sonic behavior of the pipe speech attacks and releases, the reverberation of each single note, or the variations in the sustained notes, such as due to the changes in wind supply, are also recorded.

The studio-grade multi-channel recording equipment is of the highest quality yet small enough to be easily mobilized, set up and removed. The sampling process usually takes place at night, when there is no interference with the services of the institution and the background noise is also less disturbing.

Microphone placement and multichannel audio

Microphone placement is of utmost importance and directly relates to certain engineering and aesthetic aspects. For example, if microphones are placed too close to the organ, the natural reverberation might be suppressed and the sound may be too harsh and raw, while if they are placed too far from the pipe organ, the sound can become muddy, and excessive environmental noise could undermine the desired quality. Therefore, before we do the sampling, we also conduct extensive listening tests and measurements to determine the appropriate microphone positions. We then usually record in multiple microphone positions simultaneously, up to 40 channels per recording session. We also regularly employ 3D soundfield recording techniques such as first-order or higher-order ambisonics (HOA).

Inspired Acoustics pioneered the so-called semi-dry recording technique related to microphone placement.

Sampling tremulants

In real pipe organs, tremulants are often available either on the entire organ (‘channel tremulants’), on certain divisions or on specific stops. In these cases, we record both tremulated and untremulated pipe sounds so that we can later model, if needed, pipe-by-pipe a true-to-life termulant sound, or just add the tremulant samples to the virtual pipe organ and play them back when needed. By providing the sounds, the resources of the host computer must be able to load and store them.

Measurements

Acoustics

To help further processing, various features, both visually and acoustically, must be measured in addition to the sampling process. At Inspired Acoustics, we do extensive acoustical measurements of the surrounding environment to capture the true reverberation of the space beyond the levels that our ears and microphones can normally hear because of the environmental noise covering up the decay of the sound. This is very important since quiet pipe sounds often do not produce much recordable reverberation above the noise levels, and the measurements help us see beyond what can be heard. One might ask why that is so important, and the answer is simple: in many cases, virtual pipe organs are used without the blower noise turned on, for example in film sound or music production, where dynamics exceeding what is experienced on-site are beneficial. These measurements are done using the same scientific process that we use when we do acoustical consultancy in the design or refurbishment of a music venue, concert hall or opera house.

Visuals

We also take photographs of the space and the pipe organ console to later reconstruct its visuals in 3D. Each virtual pipe organ has unique graphic interfaces, photo-realistically recreating its console, buttons, drawstops and visuals elements.

Swellboxes

Swellboxes and enclosed pipes also require measurements to allow us modeling their behavior in the organ. Acoustically, every swellbox is different, not only due to their difference in volume but also because of the materials they are made of. In this case, we measure the sound insulation of the swellboxes either by using similar standardized methods that we apply in our acoustical consultancy projects, or by employing the pipes themselves and comparing recordings of the same pipes with the swellbox shutters set in different states.

Wind models

Sounds of historic and newly-built organs in historic style often exhibit a certain behavior related to wind pressure changes as pipes consume air. In modern organs, the wind pressure is often very stable, and the wind supply is not related to what is being played, but in historic instruments, as more pipes are being engaged, the supply of air and pressure drops, affecting certain aspects of pipe speech. This is a dynamic effect that needs to be modeled in real time. Apart from what the software platform may support to model here, we also do original research related to this matter to further expand the limits of such wind modeling systems. Nevertheless, wind modeling is an important aspect of sound, and we measure such behavior on-site.

Touch sensitivity

It may sound strange at first, but many mechanical pipe organs are actually touch-sensitive. The pipe starting and ending transient, so-called pipe speech, can be quite different depending on how you play on the keys. In order to be able to model touch sensitivity, especially on tracker organs and instruments with mechanical action, we do on-site measurements and recordings. This is also an ongoing research project for us, and we cooperate with institutions and researchers to incorporate the latest results in our virtual pipe organs.

Micro-tuning and temperament

Each pipe recording is thoroughly analyzed to detect its pitch. These data are later used to determine the organ’s original temperament. This temperament is provided in the virtual pipe organ with the option of switching the organ to another temperament in real time. Several micro-tuning presets are also provided by Inspired Acoustics free of charge, usable with any organ.

Post-production

Audio processing and looping

The recorded sounds, images and measurement data are aligned together in the post-production process. First, we have a database of raw sounds – thousands of sounds for each instrument, immersed in organ blower noise and unwanted ambient sounds that need to be removed without introducing artifacts and removing useful sound components of the pipe sound. In the sound processing, Inspired Acoustics uses a proprietary methodology called SPIRAL (Synaptic Regeneration Algorithm). With SPIRAL, we can apply post-processing to a level that is manually unfeasible: hundreds of custom processing steps to each individual pipe in a time-variant manner. You can read more about SPIRAL here. This method not only helps processing organs (even instruments in not so ideal condition) in better quality than what is achievable in current commercially available software packages, but also reduces on-site recording time and contributes to a more competitive pricing of the organs.

Synchronized looping in surround

In a virtual pipe organ, you cannot tell in advance for how long a note will be held. Also, it might be unhelpful for optimum resource management to record extremely long sample files in order to make sure the actual notes are held for a shorter time and we are not running out of recorded data. To overcome this, looping is used. Looping is a process where we find starting and ending points within the files that can be repeated during playback as long as needed. Since individual pipe sounds exhibit amplitude and slight pitch changes in time, and have multiple harmonics, sometimes with changing phase, looping a single channel of audio can alone be challenging. But in order to keep the spatial image intact, we need to loop in a synchronized manner for as many channels as available. To support this, we implemented a multi-channel search tool capable of doing this task automatedly with high accuracy. 

Virtual restoration – retuning of mixtures

In many cases, pipe organs that we visit are in need of reconstruction or they are not perfectly maintained. In other cases, the very reason for our virtualization recording is to capture the last moment of the pipe organ before it is dismantled for restoration. In these cases, at a later stage, after the recording, often comes the need to retune certain pipes. Changing the pitch of a recorded pipe could easily be carried out by adjusting the playback speed, for example, but this introduces certain unwanted side effects, so more sophisticated methods are applied to compensate for this. Still, retuning individual pipes within a recording of mixtures, for instance, was long considered to be impossible. With our in-house software tools we can retune mixtures, cornet, sesquialtera and similar stops to the desired extent, just as if the organ builder was going back to retune the pipe.

Visual modeling

Life-like graphic modeling of the organ console and its stop controls is a unique feature Inspired Acoustics has first introduced to virtual pipe organs. As graphics modeling has evolved, so did our techniques. We build a 3D model of every pipe organ console that we record, and we have recently started to model every church interior as well. We combine photography and modeling as needed.

Manual and pedal compass, short and broken octaves

In organ building history, not only the number of keyboards (manuals) and pedals has changed but also the number of keys they used. Our virtual pipe organs faithfully represent the number of keys and stops available, and we also sometimes provide compass extensions to them in the virtual model, for ergonomic reasons. This often means adding higher pitched notes to keys missing on the historic instrument, to allow for playing a wider range of music. The compass provided by each virtual pipe organ is listed in each product’s features table.

In many historic organs, short octaves are provided - with some bass pipes missing and keys playing different tones than what is played in other octaves. Short octaves are also faithfully recreated in IA virtual pipe organs with an additional option to map them back, in real time, to the typical chromatic setting. This feature turned out to be very useful and educational in practicing. The missing pipes, not existing in the real organ, are created using virtually revoiced recordings of neighboring pipes.

Broken octaves (where there is a different key for D# and Eb, for example) are more difficult to implement, but can still be supported. We record all tones for these organs, too, and provide special means on the user interface of accessing these keys.

Programming console features

Virtual organs of Inspired Acoustics recreate the original stop layout, stop names and console helper functions that affect playing and performance. As opposed to mass-manufactured instruments, pipe organs are all unique and custom-made both in their specification and in their sound, but there are also similarities in, for example, combination systems, helper functions related to organ schools and building styles (such as ventils in French organs, divisional combinations in English organs) or features appearing in large modern instruments.

In order to reconstruct the features of the organ console in a virtual environment, extensive programming is needed. Each virtual organ player software platform requires a slightly different approach. For Hauptwerk-based organs, as opposed to a database-driven approach, Inspired Acoustics developed its own in-house software framework and tools to implement complex organ logic, programmatically. This allows us to faithfully recreate highly complex combination systems, couplers systems, console helper functions and other details existing on the real instrument. Many of these features first appeared in Inspired Acoustics virtual pipe organs and then later inspired other developers.

In addition to the original features, we also provide simplified and standardized functions to the organs for convenience and ergonomy. This allows, for example, a home console with 2 or 3 manuals to play an organ that originally has 5 manuals, and to seamlessly move your presets and combination files to another virtual organ console, for example in your institution, with 4 manuals.